Kevin is 57 years old and Tiffany is 9 years old. How many years will it take until Kevin is only 4 times as old as Tiffany?
Explanation: We can use the given information to write down an equation about how many years it will take. Let $y$ be the number of years that it will take. In $y$ years, Kevin will be $57 + y$ years old and Tiffany will be $9 + y$ years old. At that time, Kevin will be 4 times as old as Tiffany. Writing this information as an equation, we get: $57 + y = 4 (9 + y)$ Simplifying the right side of this equation, we get: $57 + y = 36 + 4 y$ Solving for $y$ , we get: $3 y = 21$ $y = 7$.